Process for producing polycarbonates

ABSTRACT

A continuous process for producing polycarbonates by the transesterification of didiaryl carbonates with dihydroxyaryl compounds in the presence of quaternary onium compounds is disclosed. The polycarbonates thus produced are suitable for preparing a variety of articles.

FIELD OF THE INVENTION

[0001] The present invention relates to a continuous process for producing polycarbonates, more specifically to producing polycarbonates by transesterification.

SUMMARY OF THE INVENTION

[0002] A continuous process for producing polycarbonates by the transesterification of didiaryl carbonates with dihydroxyaryl compounds in the presence of quaternary onium compounds, without the addition of basic alkali- or alkaline earth metal compounds, is disclosed. The polycarbonates thus produced are suitable for preparing a variety of articles.

BACKGROUND OF THE INVENTION

[0003] The production of aromatic oligo- or polycarbonates by the melt-transesterification process is known from the literature, and has been described previously, for example, in the Encyclopedia of Polymer Science, Vol. 10 (1969), in Chemistry and Physics of Polycarbonates, Polymer Reviews, H. Schnell, Vol. 9, John Wiley and Sons, Inc. (1964), and in DE-C 10 31 512.

[0004] In the aforementioned literature references and in the literature information described therein, basic alkali, alkaline earth and transition metal hydroxides, alcoholates, carbonates, acetates, borohydrides, hydrogen phosphates and hydrides are used as catalysts. These catalysts are chosen to enable the use of low processing temperatures and short residence times for the melts during the manufacturing process to achieve higher product qualities. However, these catalysts have the disadvantage that they catalyze secondary reactions which result in defects in the polycarbonate. Defects such as these include defect structures A-D, which are defined below in the text. In addition, the catalysts remain in the polycarbonate and can have a negative effect on the properties of the polymer because they contain impurities. The aim was therefore to produce a polycarbonate which is as pure as possible and as low colored as possible by use of an improved process.

[0005] Therefore, in order to minimize the addition of these catalysts, they are very often used in combination with onium compounds, such as those described in EP-A 673959 or EP-A 694572, for example.

[0006] EP-A 671 428 describes the production of a polycarbonate by melt transesterification, in which tetraorganophosphonium carboxylates which decompose during the production process are used as catalysts. Only a discontinuous process is described. A discontinuous process is however less susceptible to fluctuating or inadequate catalyst concentrations. These do however occur frequently in the case of such types of catalysts, since they decompose uncontrollably depending on the quality of the raw materials. The contaminations can promote or inhibit decomposition. By contrast, in a fully continuous process, even the slightest fluctuations in catalyst concentrations can produce changes in the development of molecular weight during the reaction. In a continuous process this can be compensated only very inadequately or not at all by changing the reaction conditions in order to avoid lapses in product quality. Since in the case of readily decomposable catalysts such catalytic fluctuations produce the abovementioned problems, so far no fully continuous process has become known which is effective without the use of alkali metal or alkaline earth metal catalysts.

[0007] Furthermore, the products described in EP-A 671 428 have an extremely high OH terminal group concentration of more than 1000 ppm, in addition to a broad molecular weight distribution which is manifested by the Mw/Mn ratio. It is generally known, however, that the content of remaining terminal OH groups in particular should be kept as low as possible, since they have a negative effect on thermal stability and on the stability to hydrolysis, and on the behavior of the material on aging. DE 4 238 123 A1 describes a two-stage process for the production of polycarbonates by melt transesterification using quaternary ammonium or phosphonium compounds as catalysts, in which the temperatures in the first stage are limited to 260° C. and in the second stage to 295° C. In the first stage adherence to end group ranges is required. In a discontinuous process the combination of these steps results in low contents of one type of branching agent described in the application. A continuous method of synthesis is not described.

[0008] DE A 43 12 390 describes a two-stage process in which also small contents of branching agents of the same chemical structure as disclosed in DE 4 238 123 A1 are obtained. Onium compounds are used as catalysts in the first stage, whilst alkali or alkaline earth salts are used in the second stage. In this way reaction times are shortened, so as to avoid the negative impact of high temperatures to the product quality which are well known by the person skilled in the art. A disadvantage here is the industrial cost, particularly the cost on an industrial scale for a uniform distribution of the catalysts which subsequently have to be metered into the polymer matrix in the second stage. Excess local concentrations of catalysts cannot be ruled out, however, and can result in a local concentration of highly branched products, which are then contained in the polycarbonate as sources of swelling. These swelling elements form defects in the polymer matrix and limit the use of products made therefrom. Also this reference does only disclose a batch process.

[0009] Moreover, the metal catalysts which are added in the process described in DE A 4 312 390, such as alkali and alkaline earth salts, are also disadvantageous, because they remain in the product. They have to be deactivated as soon as the polycondensation process has been finished by means of suitable additives, whereby further ions are introduced. The object of the present invention, however, is to employ polycarbonates which are substantially free from electrolytes or which at least have a low content of electrolytes, i.e. which are substantially free from ions or which at least have a low content of ions, suitable for applications in the electronics field and for storage media. In the sense of the present invention, a low content of electrolyte means polycarbonates which have an alkali and alkaline earth content<60 ppb, preferably<40 ppb, most preferably<20 ppb.

[0010] Surprisingly, it has now been found that, if suitable reactions are selected, the continues production process can result in polymers, without catalysts which contain basic alkali or alkaline earth metals containing compounds, and in several subsequent steps at high temperatures and residence times, especially at the final polycondensation step, and with economic throughputs, without this procedure resulting in an increased content of terminal OH groups, increased formation of branching agents or crosslinking and loss of colour. Moreover, in contrast to EP-A 671 428, an improved molecular weight distribution is achieved.

[0011] When catalysis is effected by catalysts which contain alkali or alkaline earth metals, the temperatures and the residence time during polycondensation are lower in the final stage. It is therefore particularly surprising that in the process according to the invention, despite increased temperatures and residence times, better product colors are obtained.

BRIEF DESCRIPTION OF THE FIGURES

[0012]FIG. 1 is a graphic representation of the residual content of DPC (diphenyl carbonate) as a function of relative viscosity and Na content.

[0013]FIG. 2 depicts yellowness index (YI) as a function of relative viscosity, Na and temperature

[0014]FIG. 3 shows the temperature in final reactor as a function of relative viscosity and Na content.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention relates to a continuous process for producing polycarbonates by the transesterification of didiaryl carbonates with dihydroxyaryl compounds, characterized in that condensation is carried out in the presence of quaternary onium compounds as catalysts, wherein the final condensation stage is effected without further addition of catalysts.

[0016] This continuous process for producing polycarbonates by the transesterification of didiaryl carbonates with dihydroxyaryl compounds is preferably characterized in that, using catalysts which can be decomposed leaving no residue, after a preliminary condensation without separation of the monohydroxyaryl compound formed, and in a plurality of subsequent flash/evaporator stages in which the temperature is increased in steps and the pressure is decreased in steps, an oligocarbonate is produced which is thereafter condensed to form the finished polycarbonate in one or more basket-type reactors subsequently used, without the addition of further amounts of the spent catalyst used or of a new, different catalyst, whilst the temperature is further increased and the pressure is further reduced. Under the selected reaction conditions the catalysts decompose essentially without leaving a residue. The term “essentially without leaving a residue” is to be understood to mean that catalyst residues, for example phosphorous containing compounds, cannot be detected in the finished polycarbonate, and the cleavage products are found practically quantitatively in the condensed vapours out of the process. The detection limit of phosphorous in polycarbonate is 1 ppm.

[0017] Over the entire process, the temperatures range between 180 and 330° C., and the pressures range between 15 bar absolute and 0.01 mbar.

[0018] In order to carry out the process, the reactants can either be melted together, or the solid dihydroxyaryl compound can be dissolved in the diaryl carbonate melt or the solid diaryl carbonate can be dissolved in the dihydroxyaryl compound melt, or both raw materials can be combined as a melt, which is preferably obtained directly from production. The residence times of the seperated melts of raw materials, particularly those of the dihydroxyaryl compound melts, are selected to be as short as possible. However the mixture of the melts could be kept for longer residence times at lower temperatures, due to the reduced melting point of the mixture compared to the separate raw materials without being damaged. Thereafter, the catalyst, dissolved in the monohydroxyaryl compound, preferably phenol, from which the diaryl carbonate is prepared, is admixed and the melt is heated to the reaction temperature. At the commencement of the technical important process of producing polycarbonate from Bisphenol A and diphenyl carbonate, the reaction temperature is 180 to 220° C., preferably 190 to 210° C., particularly preferably 190° C. At a residence time of 15 to 90 min., preferably 30 to 60 min., reaction equilibrium sets in, without removing the released monohydroxyaryl compound. The reaction can be conducted at atmospheric pressure, or can also be operated under an overpressure for industrial reasons. The preferred pressure in industrial installations is 2 to 12 bar.

[0019] The molten mixture is flashed into a first vacuum chamber, the pressure in which is set to 100 to 400 mbar, preferably 150 to 300 mbar, and directly thereafter is heated to its inlet temperature again in a suitable apparatus at the same pressure. During this expansion process the released monohydroxyaryl compound is removed together with remaining amounts of monomers.

[0020] After a residence time of 5 to 30 minutes in a receiver, optionally with circulating pump device keeping temperature and pressure constant, the reaction mixture is flashed into in a second vacuum chamber, the pressure in which is 50 to 200 mbar, preferably 80 to 150 mbar, and directly thereafter is heated to a temperature of 190 to 250° C., preferably 210 to 240° C., particularly preferably 210 to 230° C., in an apparatus at the same pressure. Again during this expansion process released monohydroxyaryl compound is removed together with remaining amounts of monomers.

[0021] After a residence time of 5 to 30 min in a receiver, optionally with circulating pump device keeping temperature and pressure constant, the reaction mixture is flashed into a third vacuum chamber, the pressure in which is 30 to 150 mbar, preferably 50 to 120 mbar, and directly thereafter is heated to a temperature of 220 to 280° C., preferably 240 to 270° C., particularly preferably 240 to 260° C., in a suitable apparatus at the same pressure. Again during this expansion process released monohydroxyaryl compound is removed together with remaining amounts of monomers.

[0022] After a residence time of 5 to 20 min in a receiver, optionally with circulating pump device keeping temperature and pressure constant, the reaction mixture is flashed into a further vacuum chamber, the pressure in which is 5 to 100 mbar, preferably 15 to 100 mbar, particularly preferably 20 to 80 mbar, and directly thereafter is heated to a temperature of 250 to 300° C., preferably 260 to 290° C., particularly preferably 260 to 280° C., in a suitable apparatus at the same pressure. Again during this expansion process released monohydroxyaryl compound is removed together with remaining amounts of monomers.

[0023] The number of these stages, which is 4 here for example, can vary between 2 and 6, preferably between 3 and 6. The relative viscosity of the oligomer which is attained in these stages ranges between 1.04 and 1.20, preferably between 1.04 and 1.15, particularly preferably between 1.05 and 1.15, very particularly preferably between 1.06 and 1.10 . The relative viscosity is determined as the ratio of the viscosity of the solvent to the viscosity of the polymer dissolved in said solvent. It was determined in dichloromethane at a concentration of 5 g/liter at 5° C.

[0024] After a residence time of 5 to 20 minutes in a receiver, optionally with circulating pump device keeping temperature and pressure constant compared to the last of the above mentioned steps, the oligomer which is thus produced is fed into a basket-type reactor and is further condensed at 250 to 310° C., preferably 250 to 290° C., particularly preferably 250 to 280° C., at pressures of 2 to 15 mbar, preferably 4 to 10 mbar, and at residence times of 30 to 90 min, preferably 30 to 60 min.

[0025] The product attains a relative viscosity of 1.12 to 1.25, preferably 1.13 to 1.22, particularly preferably 1.13 to 1.20.

[0026] The melt leaving this reactor is brought to the desired final viscosity in a basket-type reactor. The temperatures range from 270 to 330° C., preferably 280 to 320° C, particularly preferably 280 to 310° C., the pressure ranges from 0.01 to 3 mbar, preferably 0.2 to 2 mbar, at residence times of 60 to 180 min, preferably 75 to 150 min. The relative viscosities are adjusted to the values required for the application concerned and range from 1.18 to 1.40, preferably 1.18 to 1.36, particularly preferably 1.18 to 1.34.

[0027] Instead of two basket type reactors the whole final polycondensation step could also be carried out in one reactor of said type.

[0028] The vapours which come out of the different process steps are unified and reprocessed, for example according to the process disclosed in Geman Patent Application Serial number 1 01 00 404.

[0029] Depending on the course of the process, suitable apparatuses and reactors for the individual process steps include heat exchangers, apparatuses or agitated vessels which provide the requisite residence time at constant temperature; flashing apparatuses such as vessels of large volume, separators or cyclones, stirred vessels, rotary evaporators or other commercially available apparatuses; conditions which ensure the requisite residence times after heating; single- or double-shaft basket-type or disc reactors having the requisite volume and film forming areas, as well as a construction which is appropriate for the increasing melt viscosity.

[0030] The pipelines between apparatuses should of course be as short as possible, and bends in the lines should be kept as slight as possible. The general external conditions to be relied on when building facilities for chemical processes have to be taken into consideration in this respect.

[0031] In a preferred embodiment of the process, a customary heat exchanger is used for heating the molten raw materials. A perforated tray column is used as a hold-up vessel for achieving reaction equilibrium. The flashing operations, i.e. the flash evaporation operations, are carried out in centrifugal separators, preferably cyclones or baffle separators. The melt flowing out of the centrifugal separator, preferably cyclones or baffle separators is heated in falling film evaporators, which are followed by vessels for adjusting the residence time. The vessels are equipped with a circulating pump device and the melts out of the circulating pump device, centrifugal separators, preferably cyclones or baffle separators flow through a lattice construction, perforated metal sheet construction or a packed column and are collected in the sump. Condensation to form a medium viscosity product is carried out in a disc-type or basket-type reactor. Polycondensation is also effected in a disc-type or basket-type reactor, which at the high residence times provides a very large surface which is continuously renewed under vacuum. The geometric construction of the disc-type or basket-type reactors corresponds to the increase in melt viscosity. It could also be possible in certain special arrangements to use only one disc-type or basket-type reactor. Examples of suitable reactors include those which are described in WO A 99/28 370. Reactors made of materials which contain less than 5% iron are particularly suitable.

[0032] Particularly suitable materials for the production of the apparatuses, reactors, pipelines, pumps and fittings are stainless steels of type Cr Ni (Mo) 18/10, such as for example 1.4571 or 1.4541 (Stahlschlüssel 2001, Verlag: Stahlschlüssel Wegst GmbH, Th-Heuss-Straβe 36, D-71672 Marbach) and Ni base alloys of type C, such as for example 2.4605 or 2.4610 (Stahlschlüssel 2001, Verlag: Stahlschlüssel Wegst GmbH, Th-Heuss-Straβe 36, D-71672 Marbach). The stainless steels are used at process temperatures of up to about 290° C. and the Ni base alloys at process temperatures of higher than about 290° C.

[0033] The present invention also relates to the thermoplastic polycarbonates which can be obtained by the process according to the invention. These have an extremely low content of cations and anions, which are each less than 60 ppb, preferably <40 ppb, most preferably <20 ppb, wherein the cations exist as those of alkali and alkaline earth metals which can originate as impurities from the raw materials used, for example, and from phosphonium and ammonium salts, and which can also originate from abrasion or corrosion of the materials of the installation employed. Further Ion like Fe—, Ni—, Cr—, Zn—, Sn—, Mo— and Al-ions and their homologues could also be present in the raw materials or originate from abrasion or corrosion of the materials of the installation employed. In the polycarbonate according to the invention the all over content of such impurities is below 2 ppm, preferably below 1 ppm and particularly preferably below 0.5 ppm.

[0034] Such very low contents are only achieved by using raw materials of highest purity. Such highly pure compounds are only obtainable by purification procedures like recrystallization, distillation, precipitation and washing and similar procedures known in the art, for example.

[0035] The anions which are present are those of inorganic and organic acids in equivalent amounts (e.g. chloride, sulphate, carbonate, phosphate, phosphite, oxalate etc.).

[0036] The polycarbonates are also distinguished by the fact that they do not contain any detectable amounts of incorporated cleavage or decomposition products containing reactive end groups which are formed during the transesterification process. Such cleavage or decomposition products are for example isopropenyl monohydroxyaryls or dimers thereof.

[0037] The weight average molecular weights of these polycarbonates range from 15,000 to 40,000, preferably from 18,000 to 36,000, preferably from 18,000 to 34,000, wherein the weight average molecular weight is determined via the relative viscosity.

[0038] The content of terminal OH groups of these polycarbonates is 50 to 750 ppm, preferably 70 to 500 ppm, most preferably 90 to 300 ppm.

[0039] The content of defect structures A-D in the polycarbonate is determined by HPLC after complete saponification. For this purpose, the polycarbonate is saponified by boiling it with sodium methylate, and is subsequently acidified, filtered, and evaporated to dryness. The residue is dissolved in acetonitrile and is detected by HPLC.

[0040] The polycarbonate according to the invention corresponds to formula (1)

[0041] wherein the part in brackets represents a repeating structural unit, wherein M is Z or a defect structure A, B, C and/or D,

[0042] wherein Z represents an aromatic radical which is described below,

[0043] wherein defect structure A

[0044] is present in a proportion which does not exceed 800 ppm

[0045] preferably 750 ppm

[0046] most preferably 500 ppm,

[0047] wherein defect structure B

[0048] is present in a proportion which does not exceed 350 ppm

[0049] preferably 250 ppm

[0050] most preferably 70 ppm,

[0051] wherein defect structure C

[0052] is present in a proportion which does not exceed 200 ppm

[0053] preferably 150 ppm

[0054] most preferably 60 ppm,

[0055] wherein defect structure D

[0056] is present in a proportion which does not exceed 750 ppm

[0057] preferably 300 ppm

[0058] most preferably 150 ppm,

[0059] wherein Y denotes H or

[0060] wherein

[0061] R indepently from each other can denote H, or identical or different C₁-C₂₀ alkyl, C₆H₅ or C(CH₃)₂C₆H₅ groups, and

[0062] n represents 0, 1 or 2,

[0063] wherein X denotes Y or —(MOCOO)Y, and

[0064] M and Y have the meanings described above.

[0065] The sum of all the defect structures A-D should not exceed 1000 ppm, preferably 700 ppm, most preferably 550 ppm.

[0066] Compared with the prior art, the process has the following surprising advantages:

[0067] Despite decomposition of the catalyst being difficult to control, polycarbonates which have the desired molecular weights, a low content of terminal OH groups, a low content of crosslinking, not detectable amounts of compounds derived from decomposition or cleavage during the melt transesterification process and a very low content of alkali and alkaline earth metal compounds can be reproducibly obtained by this continuous process. Furthermore these polycarbonates are improved by containing amounts of residual catalyst, f. e. phosphorous containing compounds, which are below the detection limit.

[0068] Since no alkali or alkaline earth metal cations are present which would otherwise be present in the polycondensation stage, the measure of deactivating the catalyst after the formation of polycarbonate is complete, whereby further ions would be introduced, can be omitted.

[0069] The content of diaryl carbonates in the finished polycarbonate is appreciably less than when the polycondensation in the last reaction step is conducted in the presence of catalysts, for example catalysts which contain alkali or alkaline earth metals.

[0070] Defect structures which originate from secondary reactions, particularly branched structures of formulae A-D, are present only in surprisingly small amounts, and in contrast to polycarbonates otherwise obtained by the melt transesterification process, do not result in increased melt or structural viscosities., The products of the invention are thus equivalent to products obtained by the solution process.

[0071] The polycarbonate which is obtained by the process according to the invention thus differs considerably from the polycarbonates known hitherto which have been produced by the transesterification process, in which the catalyst is active over the entire process or is added for subsequent polycondensation after oligocondensation has been completed.

[0072] The attainment of a good quality product is particularly surprising, because, compared with a procedure comprising lower temperatures and shorter residence times, which is only possible here in the presence of catalysts which contain alkali and/or alkaline earth salts, it is achieved by a procedure comprising a higher temperature and longer residence times. Under conditions where the product is subjected to a higher degree of thermal stress for a longer period, however, one skilled in the art would expect a loss of quality with regard to the color of the product and the content of defect structures. Surprisingly, these problems do not occur when employing the process according to the invention. One skilled in the art who starts from the prior art with the aim of producing polycarbonates which are low in or substantially free from electrolytes by polycondensation, namely in the last step of the process, without a further addition of catalyst, would therefore scarcely imagine that this could be achieved by higher temperatures and longer residence times.

[0073] Dihydroxyaryl compounds which are suitable for the process according to the invention are those of formula (II)

HO—Z—OH  (II)

[0074] where Z is C₆₋₃₀ aromatic radical which may contain one or more aromatic nuclei, and which may be substituted and may contain aliphatic or cycloaliphatic radicals, or alkylaryl groups or hetero atoms as bridging members.

[0075] Examples of dihydroxyaryl compounds of formula (II) include

[0076] hydroquinone,

[0077] resorcinol,

[0078] dihydroxydiphenyls,

[0079] bis-(hydroxyphenyl)-alkanes,

[0080] bis-(hydroxyphenyl)-cycloalkanes,

[0081] bis-(hydroxyphenyl)-sulphides,

[0082] bis-(hydroxyphenyl)-ethers,

[0083] bis-(hydroxyphenyl)-ketones,

[0084] bis-(hydroxyphenyl)-sulphones,

[0085] bis-(hydroxyphenyl)-sulphoxides,

[0086] α,α′-bis-(hydroxyphenyl)-diisopropylbenzenes,

[0087] as well as compounds thereof which contain alkylated and halogenated nuclei.

[0088] These and other suitable dihydroxyaryl compounds are described, for example, in U.S. Pat. Nos. 3,028,365, 3,148,172, 3,275,601, 2,991,273, 3,271,367, 3,062,781, 2,970,131 and 2,999,846; in DE-A 1 570 703, 2 063 050, 2 063 052 and 2 211 0956; in French Patent Specification 1 561 518; and in the monograph by H. Schnell entitled “Chemistry and Physics of Polycarbonates”, Interscience Publishers, New York 1964 all incorporated herein by reference.

[0089] Examples of preferred dihydroxyaryl compounds include:

[0090] 4,4′-dihydroxydiphenyl,

[0091] 2,2-bis-(4-hydroxyphenyl)propane,

[0092] 2,4-bis-(4-hydroxypheny1)-2-methylbutane,

[0093] 1,1 -bis-(4-hydroxyphenyl)cyclohexane,

[0094] 1,1 -bis-(4-hydroxyphenyl)-4-methylcyclohexane,

[0095] α,α′-bis-(4-hydroxyphenyl)-p-diisopropylbenzene,

[0096] α,α′-bis-(4-hydroxyphenyl)-m-diisopropylbenzene,

[0097] bis-(4-hydroxyphenyl)sulphone,

[0098] bis-(4-hydroxyphenyl)methane,

[0099] 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,

[0100] bis-(2,6-dimethyl-4-hydroxyphenyl)propane,

[0101] bis-(4-hydroxypheny1)hexafluoropropane,

[0102] (4-hydroxyphenyl)-1-phenylethane,

[0103] (4-hydroxypheny1)diphenylmethane,

[0104] dihydroxydiphenylether,

[0105] 4,4′-thiobisphenol,

[0106] bis-(4-hydroxyphenyl)-1-(1-naphthyl)ethane,

[0107] bis-(4-hydroxyphenyl)-1-(2-naphthyl)ethane,

[0108] dihydroxy-3-(4-hydroxyphenyl)-1,1,3-trimethyl-lH-inden-5-ol,

[0109] dihydroxy-1-(4-hydroxyphenyl)-1,3,3-trimethyl-1H-inden-5-ol,

[0110] 2,2′,3,3′-tetrahydro-3,3,3′,3′-tetramethyl-1,1′-spirobi-1H-inden-5,5′-diol.

[0111] The following are particularly preferred:

[0112] resorcinol,

[0113] bis-(4-hydroxyphenyl)-1-(1-naphthyl)ethane,

[0114] bis-(4-hydroxyphenyl)-1-(2-naphthyl)ethane,

[0115] 2,2-bis-(4-hydroxyphenyl)propane

[0116] α,α′-bis-(4-hydroxyphenyl)-p-diisopropylbenzene,

[0117] α,α′-bis-(4-hydroxyphenyl)-m-diisopropylbenzene,

[0118] 1,1-bis-(4-hydroxyphenyl)cyclohexane,

[0119] bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,

[0120] bis-(4-hydroxyphenyl)diphenylmethane.

[0121] The following are most particularly preferred:

[0122] bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,

[0123] 4,4′-dihydroxydiphenyl,

[0124] 2,2-bis-(4-hydroxyphenyl)propane.

[0125] Either a dihydroxyaryl compound of formula (II) may be used, with the consequential formation of homopolycarbonates, or a plurality of dihydroxyaryl compounds of formula (II) may be used, with the consequential formation of copolycarbonates.

[0126] Dihydroxyaryl compounds which have residual contents of the monohydroxyaryl compounds from which they were produced may also be used. The monohydroxyaryl compound content thereof can be up to 20%, preferably 10%, more preferably to 5% and particularly preferably up to2%.

[0127] Didiaryl carbonates in the sense of the present invention are diary carbonates of formula (III)

[0128] and of formula (IV),

[0129] wherein R, R′ and R″, independently of each other, may represent H, or C₁-C₃₄ alkyl, cycloalkyl, C₇-C₃₄ alkaryl or C₆-C₃₄ aryl radicals which are optionally branched, for example diphenyl carbonate, butylphenyl-phenyl carbonate, di-butylphenyl carbonate, isobutylphenyl-phenyl carbonate, di-isobutylphenyl carbonate, tert-butylphenyl-phenyl carbonate, di-tert-butylphenyl carbonate, n-pentylphenyl-phenyl carbonate, di-(n-pentylphenyl) carbonate, n-hexylphenyl-phenyl carbonate, di-(n-hexylphenyl) carbonate, cyclohexylphenyl-phenyl carbonate, di-cyclohexylphenyl carbonate, phenylphenol-phenyl carbonate, di-phenylphenol carbonate, isooctylphenyl-phenyl carbonate, di-isooctylphenyl carbonate, n-nonylphenyl-phenyl carbonate, di-(n-nonylphenyl) carbonate, cumylphenyl-phenyl carbonate, di-cumylphenyl carbonate, naphthylphenyl-phenyl carbonate, di-naphthylphenyl carbonate, di-tert-butyl phenyl-phenyl carbonate, di-i-tert-butylphenyl carbonate, dicumylphenyl-phenyl carbonate, di-(dicumylphenyl) carbonate, 4-phenoxyphenyl-phenyl carbonate, di-4-phenoxyphenyl carbonate, 3-pentadecylphenyl-phenyl carbonate, di-(3-pentadecylphenyl)carbonate, tritylphenyl-phenyl carbonate, di-tritylphenyl carbonate, preferablydiphenyl carbonate, tert-butylphenyl-phenyl carbonate, di-tert-butyl phenyl carbonate, phenylphenol-phenyl carbonate, di-phenylphenol carbonate, cumylphenyl-phenyl carbonate, di-cumylphenyl carbonate, most preferably diphenyl carbonate.

[0130] The diaryl carbonates could also be used containing residual amounts of the monohydroxyaryl compound, which was used as the raw material for its manufacturing. These amounts could be up to 20% by weight of the diaryl carbonate, preferably up to 10% by weight, particularly preferably up to 5% by weight and very particularly preferably up to 2% by weight.

[0131] Furthermore, the phenolic compounds used as carbonates may also be used directly as monohydroxyaryl compounds in addition to the aforementioned carbonates, in order to influence the terminal groups of the polycarbonate. For this purpose such a monohydroxyaryl compound must be selected which posseses a boiling point above the boiling point of the monohydroxyaryl compound used as the precursor for the diaryl carbonate used in the process. The preferred mixtures are those which contain diphenyl carbonate. In the process according to the invention, it is possible to add the monohydroxyaryl compound at any time during the reaction, preferably at the start of the reaction, and the amount added may be divided into a plurality of portions. The proportion of free monohydroxyaryl compound may range from 0.4-17 mol %, preferably 1.3-8.6 mol % (with respect to the dihydroxyaryl compound). The addition may be made either before the reaction, or completely or in part during the reaction.

[0132] The diaryl carbonates are used in an amount of 1.02 to 1.30 mol, preferably 1.04 to 1.26 mol, most preferably 1.06-1.22 mol, with respect to one mole of dihydroxyaryl compound. Mixtures of the aforementioned diaryl carbonates may also be used.

[0133] Ammonium or phosphonium catalysts are used for the synthesis. For the purpose of the present application, these are also jointly designated as onium compounds. They are preferably used in amounts of 10⁻⁸ to 10⁻³ mol, most preferably in amounts of 10⁻⁷ to 10⁻⁴ mol, with respect to one mol dihydroxyaryl compound.

[0134] Phosphonium salts may be used as catalysts for the production of the polycarbonates according to the invention, and may optionally be used in combination with other suitable catalysts which do not result in too high a content of defect structures A-D and which decompose at elevated temperatures, such as other onium compounds for example.

[0135] Phosphonium salts in the sense of the invention are those of formula (VII),

[0136] wherein R¹⁻⁴ can represent identical or different C₁-C₁₀ alkyl, C₆-C₁₀ aryl, C₇-C₁₀ arylalkyl or C₅-C₆ cycloalkyl groups, preferably methyl or C₆-C₁₄ aryl groups, most preferably methyl or phenyl, and X⁻ can be an anion such as hydroxide, sulphate, hydrogen sulphate, hydrogen carbonate, carbonate, a halide, preferably chloride, or an alcoholate of formula OR, wherein R is preferably a C₆-C₁₄ aryl or a C₇-C₁₂ arylalkyl group, most preferably phenyl. Compounds such as these are described in “Houben-Weyl, Methoden der organischen Chemie”, Thieme Verlag Stuttgart, 4th Edition, 1963, Vol. 12.1, pages 47, 107-147, as thermally labile phosphonium salts. The preferred catalysts are:

[0137] tetraphenylphosphonium chloride,

[0138] tetraphenylphosphonium hydroxide,

[0139] tetraphenylphosphonium phenolate,

[0140] most preferably tetraphenylphosphonium phenolate.

[0141] Preferred amounts of phosphoniumcatalysts are 10⁻⁸ to 10⁻³ per mol of dihydroxyaryl compound, particularly preferred are amounts of 10⁻⁷ to 10⁻⁴.

[0142] The catalysts are added in solution in order to avoid damaging excess concentrations during metering. The solvents are system- and process-inherent compounds such as for example dihydroxyaryl compounds, diaryl carbonates or monohydroxyaryl compounds. Monohydroxyaryl compounds are particularly preferred since the skilled man knows that the dihydroxyaryl compounds and diaryl carbonates already change slightly and decompose at even slightly raised temperatures, in particular under the effect of the catalysts. The resulting compounds reduce the quality of the polycarbonate. In the technically important transesterification process for the production of polycarbonate the preferred compound is phenol. Phenol is also an obvious choice since the selected catalyst tetraphenylphosphonium phenate is isolated as a mixed crystal with phenol during the production process.

[0143] The ammonium and phosphonium compounds are removed by thermal decomposition. The cleavage products occur in the distillate, and catalyst residues can no longer be detected in the polycarbonate. (see Example). Most of the cleavage products consist of triphenlyphosphine and triphenlyphosphinoxide.

[0144] The polycarbonates may deliberately be branched by small amounts ranging from 0.02 to 3.6 mol % (with respect to the dihydroxy compound) of branching agents. Suitable branching agents include compounds which are suitable for the production of polycarbonate and which contain three or more functional groups, preferably those with three or more than three phenolic OH groups, for example 1,1,1-tri-(4-hydroxyphenyl)ethane and isatin-bis-cresol.

[0145] Remaining amounts of monomers in the polycarbonate which are still present due to the chemical balance of the reaction and the process parameters like temperature, pressure and residence times could be further reduced by use of suitable evaporation processes.

[0146] Adjuvant substances and reinforcing agents may be admixed with the polycarbonates according to the invention in order to modify the properties thereof. Suitable adjuvant substances and reinforcing agents include thermal and UV stabilizers, flow enhancers, demoldingagents, flame retardants, pigments, finely divided minerals, fiberous substances, e.g. alkyl and aryl phosphites, phosphates, phosphanes, low molecular weight esters of carboxylic acids, halogen compounds, salts, chalk, quartz flour, glass and carbon fibers, pigments and combinations thereof. Compounds such as these are described, for example, in WO-A 99/55772, pages 15-25, and in “Plastics Additives”, by R. Gachter and H. Müller, Hanser Publishers 1983, incorporated herein by reference.

[0147] Furthermore, other polymers may also be admixed with the polycarbonates according to the invention, e.g. polyolefins, polyurethanes, polyesters, acrylonitrile-butadiene-styrene and polystyrene.

[0148] These substances are preferably added to the finished polycarbonate in conventional processing units, but may be added during a different stage of the production process depending on the requirements.

[0149] The polycarbonates obtained by the process according to the invention may be processed in the usual manner in customary machines, e.g. in extruders or injection molding machines, to form moldings such as sheet or slabs.

[0150] Applications of the polycarbonates according to the invention include:

[0151] 1. Safety glass panes or sheets, which, as is known, are necessary in many areas of buildings, vehicles and aircraft, and which are also used for the visors of helmets.

[0152] 2. The production of extruded sheeting and sheeting formed from solution for displays or electric motors, and also sheeting for skiing.

[0153] 3. The production of blown articles (se U.S. Pat. No. 2,964,794, for example).

[0154] 4. The production of transparent sheeting, particularly cavity sheeting, for the cladding of buildings such as railway stations, greenhouses and lighting installations.

[0155] 5. The production of traffic light housings or traffic signs.

[0156] 6. The production of foamed materials (see DE-B 1 031 507, for example).

[0157] 7. The production of fibers and filaments (see DE-B 1137 167 and DE-A 1 785 137, for example).

[0158] 8. Translucent plastics with a content of glass fibers for photometric purposes (see DE-A 1 554 020, for example).

[0159] 9. The production of precision injection molded parts, such as lens holders for example. Polycarbonate with a content of glass fibers is used for this purpose, and optionally additionally contains about 1-10% by weight MoS₂with respect to its total weight.

[0160] 10. Optical applications such as optical storage media (CDs, DVDs), safety spectacles, or lenses for photographic and film cameras (see DE-A 2701173, for example).

[0161] 11. Light transmission supports, particularly optical fiber cables (see EP-A1 0089 801, for example).

[0162] 12. Electrical insulation materials for electrical conductors and for plug housings and plug-in connectors.

[0163] 13. As a support material for organic photoconductors.

[0164] 14. The production of lamps, e.g. headlamps, lens covers or lamp covers.

[0165] 15. Medical applications, e.g. oxygenators, dialysers.

[0166] 16. Foodstuff applications, such as bottles, crockery and chocolate moulds.

[0167] 17. Applications in the automobile field, where contact with fuels and lubricants can occur.

[0168] 18. Articles for sports, such as slalom poles for example.

[0169] 19. Domestic articles such as kitchen sinks and letterbox housings.

[0170] 20. For casings, e.g. electricity distribution boxes, electrical appliances, domestic appliances.

[0171] 21. Components of domestic articles and of electrical and electronic appliances.

[0172] 22. The production of motorcycle- and safety helmets.

[0173] 23. Parts of automobiles, such as window glass, dashboards, bodywork parts and shock absorbers.

[0174] 24. Other applications such as feeding doors for stables or animal cages.

[0175] In particular, the polycarbonates according to the invention are suitable for use in the field of electronics, especially for optical, magneto-optic and other data storage media.

[0176] The present invention also relates to products made from the polycarbonates according to the invention.

EXAMPLES Example 1

[0177]94.7 kg/hour of a molten mixture consisting of 49.8 kg diphenyl carbonate/hour (232.7 mol/hour) and 44.9 kg bisphenol A/hour (196.9 mol/hour), with the addition of 0.0034 kg tetraphenylphosphonium phenolate/hour (0.0079 mol/hour) dissolved in 0.1 kg phenol/hour were pumped from a container through a heat exchanger, and were heated to 190° C. and passed through a hold-up column. The mean residence time was 45 minutes.

[0178] The melt was then led, via a flashing valve, into a separator at a pressure of 200 mbar. The melt flowing therefrom was heated to 190° C. again in a falling film evaporator, which was also maintained at 200 mbar, and was caught in a container. After a residence time of 20 minutes, the melt was pumped into the next three stages of identical construction. The conditions in the 2^(nd)/3^(rd)/4^(th) stages were 80/50/25 mbar; 230/250/270° C. and 20/10/10 minutes. The oligomer formed had relative viscosity of 1.068. All the vapors were passed via pressure controllers into a column maintained under vacuum, and were taken off as a condensate.

[0179] The oligomer was subsequently condensed in a basket-type reactor at 270° C. and 7.3 mbar, and at a residence time of 45 minutes, to form a high molecular weight oligomer. The relative viscosity thereof was 1.134. The vapors were condensed.

[0180] The oligomer was condensed in a further basket-type reactor at 311° C. and 1.0 mbar to give a relative viscosity of 1.277. The mean residence time was determined as 130 minutes. The vapors were thereby condensed after passing or inside of the vacuum system.

[0181] The polycarbonate contains 245 ppm of terminal OH-groups and the following contents of branched species were measured in the polycarbonate: structure A: 226 ppm; structure B: 6 ppm; structure C:<5 ppm; structure D: 138 ppm.

[0182] An amount of phosphorus corresponding to 0.000234 kg/hour was detected in the combined condensates from the vapor streams. This was equivalent to 96.3% of the amount of catalyst used (=0.000243 kg/hour). Accordingly, no significant amounts of catalyst residues or decomposition products remained in the product. Phosphorous could not be detected.

Examples 2 to 8

[0183] By varying the ratio of diphenyl carbonate to bisphenol A, polycarbonates were produced which contained comparable terminal groups but which had different relative viscosities. Apart from the vacuum, all the conditions such as throughput, catalyst and temperature remained constant in these tests. The results are given in Table 1. TABLE 1 Temp. of Rel. ppm ppb final Test viscosity OH Na reactor YI ppm DPC 2 1.202 290 0 310 3.54 553 3 1.203 280 0 310 3.77 534 4 1.218 290 0 310 3.23 444 5 1.253 290 0 310 3.00 268 6 1.274 280 0 310 2.92 217 7 1.277 230 0 311 2.77 227 8 1.287 250 0 311 2.69 195

[0184] DPC denotes diphenyl carbonate.

Comparative Examples 9 to 14

[0185] In a further series of tests, the same solution of tetra-phenylphosphonium phenolate in phenol, which was enriched with different amounts of sodium phenolate/hour, however, was fed into the molten mixture. The corresponding amounts, and the equivalent amount of sodium in ppb with respect to polycarbonate, are listed in Table 2. By varying the ratio of diphenyl carbonate to bisphenol A, polycarbonates were produced which contained comparable terminal groups but which had different relative viscosities. These further results are given in Table 2. TABLE 2 Corresponding amount (g) of Temp. Rel. ppm Na ppb of final ppm Test viscosity OH phenolate/hour Na reactor YI DPC  9 1.207 290 0.0630 250 290 3.69 585 10 1.249 310 0.0315 125 310 3.77 378 11 1.251 310 0.0630 250 300 3.84 348 12 1.276 290 0.0630 250 310 4.00 288 13 1.287 260 0.0252 100 310 3.54 260 14 1.292 250 0.0252 100 310 3.38 232

[0186] The test results are illustrated in FIGS. 1 to 3.

[0187] Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims. 

What is claimed is:
 1. A continuous process for producing polycarbonate comprising transesterifying didiaryl carbonate with dihydroxyaryl compound, and condensing in the presence of a quaternary onium compound catalyst, said condensing including a final stage, said process characterized in the absence of additional catalyst from said final stage.
 2. A continuous process for producing polycarbonate according to claim 1, wherein a essentially readily decomposable onium compound is used as a catalyst and in which after a precondensation without removing the released monohydroxyaryl compound an oligocarbonate is formed in subsequent evaporation steps by stepwise reduction of pressure and stepwise rise of temperature removing the released monohydroxyaryl compound, which is then further condensed to the final product in one or more basket-type reactors without adding further catalysts again by evaporating the monohydroxyaryl compound using a stepwise reduction of pressure and stepwise rise of temperature.
 3. The polycarbonate prepared by the the process according to claim
 1. 4. The polycarbonate of according to claim 2, characterized in being substantially free of electrolytes.
 5. A storage medium comprising the polycarbonate of claim
 2. 6. Optical storage medium comprising the polycarbonate of claim
 2. 7. Magneto-optic storage medium comprising the polycarbonate of claim
 2. 8. The process of claim 1 wherein onium compound is tetraphenylphosphonium phenolate.
 9. The process of claim 1 wherein catalyst is used in an amount of 10⁻⁸ to 10⁻³ mol per one mol bisphenol.
 10. The process of claim 9 wherein the catalyst is used in an amount of 10⁻⁸ to 10⁻³ mol per one mol bisphenol.
 11. The process of claim 1 wherein the catalyst is added dissolved in phenol.
 12. The process of claim 1 wherein the apparatuses, reactors, pipelines, pumps and fittings which are used at process temperatures of up to about 290° C. are made of stainless steels of type Cr Ni (Mo) 18/10 and the ones used at process temperatures of higher than about 290° C. are made of Ni base alloys of type C. 